Haruka Shigi is a supporting character and an Ashikabi, a human with the ability to form a contract with super-powered beings known as Sekirei. He is a young man of average height and slim build, standing at 166 centimeters, with a weight of 54 kilograms. He has messy brown hair that reaches to his neck and green eyes, and is typically seen wearing casual clothes such as a white shirt and blue jeans, sometimes with a blue jacket. He is twenty years old and was born on August 9. In his personal life, Shigi is a ronin, a student who has failed university entrance examinations and is studying to try again. In this regard, he shares a deep commonality with the protagonist, Minato Sahashi, as both have failed the entrance exam for Shinto Teito University twice and are preparing for a third attempt. This shared experience leads Minato to jokingly refer to Shigi as his soulmate, and it is the foundation for a long-lasting and loyal friendship between the two men.

In terms of personality, Shigi is generally amicable and kind, but he possesses a hair-trigger temper. He is easily irritated by condescending remarks from others, such as those made by the Ashikabi Seo Kaoru. Furthermore, he becomes fiercely protective and angry when he perceives an attack on someone he cares about, for example, when a Sekirei named Benitsubasa mistreats Minato. This fiery and defensive nature is most profoundly displayed in his relationship with his own Sekirei, a young woman named Kuno. Shigi often laments his situation and compares Kuno unfavorably to other, more combat-capable Sekirei. However, these remarks do not stem from malice or a lack of affection. In truth, he loves Kuno deeply and is utterly devoted to her protection. His primary motivation throughout his appearance in the story is to ensure her safety, even though she possesses very little useful fighting ability. Driven by this desire to defend her, Shigi decides to withdraw from the Sekirei Plan, a dangerous battle royale, by fleeing the city of Tokyo before the project's overseeing organization, MBI, can stop them. To this end, he seeks and receives help from his friends Minato and Seo to formulate an escape plan.

Shigi's role in the narrative centers on this major attempt to escape. He lives in the same apartment complex where Minato previously resided, which further cements their connection. The key relationship in his life is undoubtedly with Kuno, whom he constantly worries about due to her vulnerability. His love for her is not conditional on her strength, and he proves his courage by standing between her and far more powerful adversaries, including members of the feared Disciplinary Squad, who are among the strongest Sekirei in the city. Using a strategy devised by Seo, Shigi and Kuno attempt to cross an unguarded railroad bridge on the northern edge of the city. The escape is harrowing, and despite having their path blocked by two members of the Disciplinary Squad, they are ultimately able to flee Tokyo successfully with some assistance. This act of defiance has consequences, as his successful escape later becomes a known incident, leading to even stricter border surveillance for others. Shigi's personal journey shows significant development from being a frustrated and fearful Ashikabi who wants to hide from the battle to someone who takes bold, decisive action to create a new life for himself and the woman he loves. He and Kuno later send a letter from their new life, indicating they have successfully left the Sekirei Plan behind. He does not possess any combat abilities himself, as Ashikabi are typically ordinary humans. Instead, his notable trait is his unwavering will to protect his partner, a form of courage that allows him to face overwhelming danger without any physical power to back it up.